α-Amino acids have significant biochemical importance, and are frequently used as a raw material for drugs such as antibiotics, antineoplastic agents, and enzyme inhibitors. There are natural and non-naturally occurring α-amino acids, and many useful α-amino acids of both types have been found. In recent years, there have been a series of discoveries of non-naturally occurring, beneficial physiologically active amino acids such as L-dopa and L-azatyrosine, and there is a need for research into the practical asymmetrical synthesis of such optically-active α-amino acids.
One option for the practical asymmetrical synthesis of optically-active α-amino acids is asymmetrical mono-substitution alkylation. In conventional practice, it has been common to use a ketimine-type Schiff base for asymmetrical mono-substitution alkylation (O'Donnell, M. J. et al., J. Am. Chem. Soc., 1989, vol. 111, p. 2353). Ketimine-type Schiff bases are complex to manufacture and thus generally are expensive. This has caused α-amino acids that are produced by asymmetrical mono-substitution alkylation to be expensive as well.
The reason why ketimine-type Schiff bases are used shall be explained based on the characteristics of ketimine-type Schiff bases that contribute to the reaction. Schiff bases include ketimine-type Schiff bases and aldimine-type Schiff bases, for example. In general, it is strongly believed that aldimine-type Schiff bases result in a racemization of the product because there is almost no pKa difference between the secondary hydrogen and the tertiary hydrogen, whereas ketimine-type Schiff bases inhibit racemization of the product obtained because this difference is large (O'Donnell, M. J., Aldrichim. Acta., 2001, vol. 34, p. 3, and Maruoka, K. and Ooi, T., Chemical Reviews, 2003, vol. 103, p. 3013).
Thus, in this technical field, based on the presumption that ketimine-type Schiff bases will be used in consideration of the overall production efficiency, even though production costs are somewhat higher, attention has been focused on optimizing the methods for asymmetrical synthesis of optically-active α-amino acids using ketimine-type Schiff bases.

On the other hand, recently, there was a report of an example of asymmetrical synthesis using macromolecular aldimine (Park, H.-G. et al., J. Org. Chem., 2005, vol. 70, p. 1904). However, this report pertains to asymmetrical synthesis using a compound obtained by binding aldimine to a macromolecule, and is quite different from the Schiff bases of the technical field.